A variable-color region (106) of a football-playing or baseball/softball-playing structure of an information-presentation structure extends to an exposed surface (102) at a surface zone (112) and normally appears along it as a principal color. An impact-dependent portion (138) of the variable-color region responds to an object (104) impacting the zone at an object-contact area (116) by temporarily appearing along a closely matching print area (118) of the zone as changed color materially different from the principal color. For football, the zone typically adjoins an end or side line (1446 or 1448) to help determine whether the object, typically a person's shoe, impacted the surface “in” or “out”. For baseball/softball, the zone typically adjoins a foul line (1506) to help determine whether the object, a baseball/softball, impacted the surface “fair” or “foul”.